Go: fix string formatting in error messages

As a hint whether values are eaten.

.clang-format

@@ -0,0 +1,15 @@
+BasedOnStyle: GNU
+ColumnLimit: 80
+IndentWidth: 4
+TabWidth: 4
+UseTab: ForContinuationAndIndentation
+BreakBeforeBraces: Attach
+BreakBeforeBinaryOperators: None
+SpaceAfterCStyleCast: true
+AlignAfterOpenBracket: DontAlign
+AlignEscapedNewlines: DontAlign
+AlignOperands: DontAlign
+AlignConsecutiveMacros: Consecutive
+AllowAllArgumentsOnNextLine: false
+AllowAllParametersOfDeclarationOnNextLine: false
+IndentGotoLabels: false

.gitignore

@@ -9,3 +9,5 @@
 /ell.files
 /ell.creator*
 /ell.includes
+/ell.cflags
+/ell.cxxflags

LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2017, Přemysl Janouch <p@janouch.name>
+Copyright (c) 2017, Přemysl Eric Janouch <p@janouch.name>
 
 Permission to use, copy, modify, and/or distribute this software for any
 purpose with or without fee is hereby granted.

README.adoc

@@ -59,7 +59,7 @@ When evaluating a command, the first argument is typically a string with its
 name and it is resolved as if `set` was called on it.  Lists are left for
 execution as they are.
 
-The last expression in a block is the return value.
+The last expression in a block is the block's return value.
 
 Special Forms
 -------------
@@ -172,13 +172,16 @@ Install development packages for GNU Readline to get a REPL for toying around:
  $ make repl
  $ ./repl
 
+The Go port can be built using standard Go tools and behaves the same.
+
 Possible Ways of Complicating
 -----------------------------
  * `local [_a _b _rest] @args` would elegantly solve the problem of varargs,
    that is, unpack a list when names are list, and make the last element a list
    when there are more arguments than names
- * reference counting: currently all values are always copied as needed, which
-   is good enough for all imaginable use cases, simpler and less error-prone
+ * reference counting: in the C version, currently all values are always copied
+   as needed, which is good enough for all imaginable use cases, simpler and
+   less error-prone
 
 Contributing and Support
 ------------------------

cmd/interpreter/main.go

@@ -1,5 +1,5 @@
 //
-// Copyright (c) 2018, Přemysl Janouch <p@janouch.name>
+// Copyright (c) 2018, Přemysl Eric Janouch <p@janouch.name>
 //
 // Permission to use, copy, modify, and/or distribute this software for any
 // purpose with or without fee is hereby granted.
@@ -49,15 +49,11 @@ func main() {
 		os.Exit(1)
 	}
 
-	var args *ell.V
-	tail := &args
+	var args []ell.V
 	for i := 2; i < len(os.Args); i++ {
-		*tail = ell.NewString([]byte(os.Args[i]))
-		tail = &(*tail).Next
+		args = append(args, *ell.NewString(os.Args[i]))
 	}
-
-	var result *ell.V
-	if !L.EvalBlock(program, args, &result) {
+	if _, ok := L.EvalBlock(program, args); !ok {
 		fmt.Printf("%s: %s\n", "runtime error", L.Error)
 	}
 }

cmd/repl/main.go

@@ -1,5 +1,5 @@
 //
-// Copyright (c) 2018, Přemysl Janouch <p@janouch.name>
+// Copyright (c) 2018, Přemysl Eric Janouch <p@janouch.name>
 //
 // Permission to use, copy, modify, and/or distribute this software for any
 // purpose with or without fee is hereby granted.
@@ -28,9 +28,8 @@ import (
 	"janouch.name/ell/ell"
 )
 
-func run(L *ell.Ell, program *ell.V) {
-	var result *ell.V
-	if !L.EvalBlock(program, nil, &result) {
+func run(L *ell.Ell, program []ell.V) {
+	if result, ok := L.EvalBlock(program, nil); !ok {
 		fmt.Printf("\x1b[31m%s: %s\x1b[0m\n", "runtime error", L.Error)
 		L.Error = ""
 	} else {
@@ -39,21 +38,23 @@ func run(L *ell.Ell, program *ell.V) {
 	}
 }
 
-func complete(L *ell.Ell, line string) (res []string) {
-	// This never actually completes anything, just shows the options,
-	// we'd have to figure out the longest common prefix.
-	res = append(res, line)
+func complete(L *ell.Ell, line string, pos int) (
+	head string, completions []string, tail string) {
+	tail = string([]rune(line)[pos:])
 
-	line = strings.ToLower(line)
-	for v := L.Globals; v != nil; v = v.Next {
-		name := string(v.Head.String)
+	lastSpace := strings.LastIndexAny(string([]rune(line)[:pos]), " ()[]{};\n")
+	if lastSpace > -1 {
+		head, line = line[:lastSpace+1], line[lastSpace+1:]
+	}
+
+	for name := range L.Globals {
 		if strings.HasPrefix(strings.ToLower(name), line) {
-			res = append(res, name)
+			completions = append(completions, name)
 		}
 	}
 	for name := range L.Native {
 		if strings.HasPrefix(strings.ToLower(name), line) {
-			res = append(res, name)
+			completions = append(completions, name)
 		}
 	}
 	return
@@ -66,7 +67,10 @@ func main() {
 	}
 
 	line := liner.NewLiner()
-	line.SetCompleter(func(line string) []string { return complete(L, line) })
+	line.SetWordCompleter(func(line string, pos int) (
+		string, []string, string) {
+		return complete(L, line, pos)
+	})
 	line.SetMultiLineMode(true)
 	line.SetTabCompletionStyle(liner.TabPrints)
 

ell.c

@@ -1,7 +1,7 @@
 /*
  * ell.c: an experimental little language
  *
- * Copyright (c) 2017, Přemysl Janouch <p@janouch.name>
+ * Copyright (c) 2017, Přemysl Eric Janouch <p@janouch.name>
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted.
@@ -16,14 +16,14 @@
  *
  */
 
+#include <ctype.h>
+#include <errno.h>
+#include <setjmp.h>
+#include <stdarg.h>
+#include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <ctype.h>
-#include <errno.h>
-#include <stdarg.h>
-#include <stdbool.h>
-#include <setjmp.h>
 
 #if defined __GNUC__
 #define ELL_ATTRIBUTE_PRINTF(x, y) __attribute__ ((format (printf, x, y)))
@@ -188,9 +188,18 @@ ell_list (struct ell_v *head) {
 
 // --- Lexer -------------------------------------------------------------------
 
-enum ell_token { ELLT_ABORT,  ELLT_LPAREN, ELLT_RPAREN,
-	ELLT_LBRACKET, ELLT_RBRACKET, ELLT_LBRACE, ELLT_RBRACE,
-	ELLT_STRING, ELLT_NEWLINE, ELLT_AT };
+enum ell_token {
+	ELLT_ABORT,
+	ELLT_LPAREN,
+	ELLT_RPAREN,
+	ELLT_LBRACKET,
+	ELLT_RBRACKET,
+	ELLT_LBRACE,
+	ELLT_RBRACE,
+	ELLT_STRING,
+	ELLT_NEWLINE,
+	ELLT_AT
+};
 
 static const char *ell_token_names[] = {
 	[ELLT_ABORT]    = "end of input",
@@ -240,8 +249,8 @@ ell_lexer_advance (struct ell_lexer *self) {
 static bool
 ell_lexer_hexa_escape (struct ell_lexer *self, struct ell_buffer *output) {
 	const char *abc = "0123456789abcdef", *h, *l;
-	if (!self->len || !(h = strchr (abc, tolower (ell_lexer_advance (self))))
-	 || !self->len || !(l = strchr (abc, tolower (ell_lexer_advance (self)))))
+	if (!self->len || !(h = strchr (abc, tolower (ell_lexer_advance (self)))) ||
+		!self->len || !(l = strchr (abc, tolower (ell_lexer_advance (self)))))
 		return false;
 
 	ell_buffer_append_c (output, (h - abc) << 4 | (l - abc));
@@ -254,7 +263,8 @@ enum {
 	ELL_LEXER_COMMENT = '#'
 };
 
-static bool ell_lexer_is_whitespace (int c) {
+static bool
+ell_lexer_is_whitespace (int c) {
 	return !c || c == ' ' || c == '\t' || c == '\r';
 }
 
@@ -326,13 +336,12 @@ ell_lexer_next (struct ell_lexer *self, const char **e) {
 	enum ell_token token = ell_lexer_tokens[c];
 	if (!token) {
 		ell_buffer_append_c (&self->string, c);
-		while (self->len && !ell_lexer_is_whitespace (*self->p)
-			&& !ell_lexer_tokens[*self->p])
+		while (self->len && !ell_lexer_is_whitespace (*self->p) &&
+			!ell_lexer_tokens[*self->p])
 			ell_buffer_append_c (&self->string, ell_lexer_advance (self));
 		return ELLT_STRING;
 	}
-	if (token == ELLT_STRING
-	 && (*e = ell_lexer_string (self, &self->string)))
+	if (token == ELLT_STRING && (*e = ell_lexer_string (self, &self->string)))
 		return ELLT_ABORT;
 	return token;
 }
@@ -369,8 +378,8 @@ static bool
 ell_print_string_needs_quoting (struct ell_v *s) {
 	for (size_t i = 0; i < s->len; i++) {
 		unsigned char c = s->string[i];
-		if (ell_lexer_is_whitespace (c) || ell_lexer_tokens[c]
-		 || c == ELL_LEXER_ESCAPE || c < 32)
+		if (ell_lexer_is_whitespace (c) || ell_lexer_tokens[c] ||
+			c == ELL_LEXER_ESCAPE || c < 32)
 			return true;
 	}
 	return s->len == 0;
@@ -426,8 +435,8 @@ ell_print_block (struct ell_printer *printer, struct ell_v *list) {
 
 static bool
 ell_print_set (struct ell_printer *printer, struct ell_v *list) {
-	if (!list->head || strcmp (list->head->string, "set")
-	 || !list->head->next || list->head->next->next)
+	if (!list->head || strcmp (list->head->string, "set") ||
+		!list->head->next || list->head->next->next)
 		return false;
 
 	printer->putchar (printer, '@');
@@ -448,10 +457,10 @@ ell_print_list (struct ell_printer *printer, struct ell_v *list) {
 
 static void
 ell_print_v (struct ell_printer *printer, struct ell_v *v) {
-	if (ell_print_string (printer, v)
-	 || ell_print_block (printer, v)
-	 || ell_print_set (printer, v)
-	 || ell_print_list (printer, v))
+	if (ell_print_string (printer, v) ||
+		ell_print_block (printer, v) ||
+		ell_print_set (printer, v) ||
+		ell_print_list (printer, v))
 		return;
 
 	printer->putchar (printer, '(');
@@ -563,7 +572,7 @@ ell_parse_prefix_list (struct ell_v *seq, const char *name) {
 	return ell_list (prefix);
 }
 
-static struct ell_v * ell_parse_line (struct ell_parser *p, jmp_buf out);
+static struct ell_v *ell_parse_line (struct ell_parser *p, jmp_buf out);
 
 static struct ell_v *
 ell_parse_v (struct ell_parser *p, jmp_buf out) {
@@ -576,8 +585,7 @@ ell_parse_v (struct ell_parser *p, jmp_buf out) {
 
 	SKIP_NL ();
 	if (ACCEPT (ELLT_STRING))
-		return CHECK (ell_string
-			(p->lexer.string.s, p->lexer.string.len));
+		return CHECK (ell_string (p->lexer.string.s, p->lexer.string.len));
 	if (ACCEPT (ELLT_AT)) {
 		result = ell_parse_v (p, out);
 		return CHECK (ell_parse_prefix_list (result, "set"));
@@ -706,8 +714,8 @@ static bool
 ell_scope_prepend (struct ell *ell, struct ell_v **scope, const char *name,
 	struct ell_v *v) {
 	struct ell_v *key, *pair;
-	if (!ell_check (ell, (key = ell_string (name, strlen (name))))
-	 || !ell_check (ell, (pair = ell_list (key)))) {
+	if (!ell_check (ell, (key = ell_string (name, strlen (name)))) ||
+		!ell_check (ell, (pair = ell_list (key)))) {
 		ell_free_seq (v);
 		return false;
 	}
@@ -793,19 +801,21 @@ ell_can_modify_error (struct ell *ell) {
 	return !ell->memory_failure && ell->error[0] != '_';
 }
 
-static bool ell_eval_statement (struct ell *, struct ell_v *, struct ell_v **);
+static bool ell_eval_statement
+	(struct ell *, const struct ell_v *, struct ell_v **);
 static bool ell_eval_block
-	(struct ell *, struct ell_v *, struct ell_v *, struct ell_v **);
+	(struct ell *, const struct ell_v *, struct ell_v *, struct ell_v **);
 
 static bool
-ell_eval_args (struct ell *ell, struct ell_v *args, struct ell_v **result) {
+ell_eval_args (struct ell *ell,
+	const struct ell_v *args, struct ell_v **result) {
 	size_t i = 0;
 	struct ell_v *res = NULL, **out = &res;
 	for (; args; args = args->next) {
 		struct ell_v *evaluated = NULL;
 		// Arguments should not evaporate, default to a nil value
-		if (!ell_eval_statement (ell, args, &evaluated)
-		 || (!evaluated && !ell_check (ell, (evaluated = ell_list (NULL)))))
+		if (!ell_eval_statement (ell, args, &evaluated) ||
+			(!evaluated && !ell_check (ell, (evaluated = ell_list (NULL)))))
 			goto error;
 		ell_free_seq (evaluated->next);
 		evaluated->next = NULL;
@@ -828,7 +838,7 @@ error:
 }
 
 static bool
-ell_eval_native (struct ell *ell, const char *name, struct ell_v *args,
+ell_eval_native (struct ell *ell, const char *name, const struct ell_v *args,
 	struct ell_v **result) {
 	struct ell_native_fn *fn = ell_native_find (ell, name);
 	if (!fn)
@@ -844,8 +854,8 @@ ell_eval_native (struct ell *ell, const char *name, struct ell_v *args,
 }
 
 static bool
-ell_eval_resolved (struct ell *ell, struct ell_v *body, struct ell_v *args,
-	struct ell_v **result) {
+ell_eval_resolved (struct ell *ell,
+	const struct ell_v *body, const struct ell_v *args, struct ell_v **result) {
 	// Resolving names recursively could be pretty fatal, let's not do that
 	if (body->type == ELL_STRING)
 		return ell_check (ell, (*result = ell_clone (body)));
@@ -855,13 +865,16 @@ ell_eval_resolved (struct ell *ell, struct ell_v *body, struct ell_v *args,
 }
 
 static bool
-ell_eval_value (struct ell *ell, struct ell_v *body, struct ell_v **result) {
-	struct ell_v *args = body->next;
+ell_eval_value (struct ell *ell, const struct ell_v *body,
+	struct ell_v **result) {
+	const struct ell_v *args = body->next;
 	if (body->type == ELL_STRING) {
 		const char *name = body->string;
-		if (!strcmp (name, "block"))
-			return (!args || ell_check (ell, (args = ell_clone_seq (args))))
-				&& ell_check (ell, (*result = ell_list (args)));
+		if (!strcmp (name, "block")) {
+			struct ell_v *cloned = NULL;
+			return (!args || ell_check (ell, (cloned = ell_clone_seq (args))))
+				&& ell_check (ell, (*result = ell_list (cloned)));
+		}
 		if ((body = ell_get (ell, name)))
 			return ell_eval_resolved (ell, body, args, result);
 		return ell_eval_native (ell, name, args, result);
@@ -884,15 +897,14 @@ ell_eval_value (struct ell *ell, struct ell_v *body, struct ell_v **result) {
 }
 
 static bool
-ell_eval_statement
-	(struct ell *ell, struct ell_v *statement, struct ell_v **result) {
+ell_eval_statement (struct ell *ell, const struct ell_v *statement,
+	struct ell_v **result) {
 	if (statement->type == ELL_STRING)
 		return ell_check (ell, (*result = ell_clone (statement)));
 
 	// Executing a nil value results in no value.  It's not very different from
 	// calling a block that returns no value--it's for our callers to resolve.
-	if (!statement->head
-	 || ell_eval_value (ell, statement->head, result))
+	if (!statement->head || ell_eval_value (ell, statement->head, result))
 		return true;
 
 	ell_free_seq (*result);
@@ -913,8 +925,8 @@ ell_eval_statement
 
 static bool
 args_to_scope (struct ell *ell, struct ell_v *args, struct ell_v **scope) {
-	if (!ell_check (ell, (args = ell_list (args)))
-	 || !ell_scope_prepend (ell, scope, "args", args))
+	if (!ell_check (ell, (args = ell_list (args))) ||
+		!ell_scope_prepend (ell, scope, "args", args))
 		return false;
 
 	size_t i = 0;
@@ -922,8 +934,8 @@ args_to_scope (struct ell *ell, struct ell_v *args, struct ell_v **scope) {
 		char buf[16] = "";
 		(void) snprintf (buf, sizeof buf, "%zu", ++i);
 		struct ell_v *copy = NULL;
-		if ((args && !ell_check (ell, (copy = ell_clone (args))))
-		 || !ell_scope_prepend (ell, scope, buf, copy))
+		if ((args && !ell_check (ell, (copy = ell_clone (args)))) ||
+			!ell_scope_prepend (ell, scope, buf, copy))
 			return false;
 	}
 	return ell_check (ell, (*scope = ell_list (*scope)));
@@ -931,7 +943,7 @@ args_to_scope (struct ell *ell, struct ell_v *args, struct ell_v **scope) {
 
 /// Execute a block and return whatever the last statement returned, eats args
 static bool
-ell_eval_block (struct ell *ell, struct ell_v *body, struct ell_v *args,
+ell_eval_block (struct ell *ell, const struct ell_v *body, struct ell_v *args,
 	struct ell_v **result) {
 	struct ell_v *scope = NULL;
 	if (!args_to_scope (ell, args, &scope)) {
@@ -961,13 +973,14 @@ ell_eval_block (struct ell *ell, struct ell_v *body, struct ell_v *args,
 	(struct ell *ell, struct ell_v *args, struct ell_v **result)
 
 static bool
-ell_eval_any (struct ell *ell, struct ell_v *body, struct ell_v *arg,
-	struct ell_v **result) {
+ell_eval_any (struct ell *ell,
+	const struct ell_v *body, const struct ell_v *arg, struct ell_v **result) {
 	if (body->type == ELL_STRING)
 		return ell_check (ell, (*result = ell_clone (body)));
-	if (arg && !ell_check (ell, (arg = ell_clone (arg))))
+	struct ell_v *cloned_arg = NULL;
+	if (arg && !ell_check (ell, (cloned_arg = ell_clone (arg))))
 		return false;
-	return ell_eval_block (ell, body->head, arg, result);
+	return ell_eval_block (ell, body->head, cloned_arg, result);
 }
 
 static struct ell_v *
@@ -1025,8 +1038,8 @@ ell_defn (ell_fn_local) {
 	struct ell_v *values = names->next;
 	for (names = names->head; names; names = names->next) {
 		struct ell_v *value = NULL;
-		if ((values && !ell_check (ell, (value = ell_clone (values))))
-		 || !ell_scope_prepend (ell, scope, names->string, value))
+		if ((values && !ell_check (ell, (value = ell_clone (values)))) ||
+			!ell_scope_prepend (ell, scope, names->string, value))
 			return false;
 		if (values)
 			values = values->next;
@@ -1041,9 +1054,9 @@ ell_defn (ell_fn_set) {
 
 	struct ell_v *v;
 	if ((v = name->next))
-		return ell_check (ell, (v = ell_clone (v)))
-			&& ell_check (ell, (*result = ell_clone (v)))
-			&& ell_set (ell, name->string, v);
+		return ell_check (ell, (v = ell_clone (v))) &&
+			ell_check (ell, (*result = ell_clone (v))) &&
+			ell_set (ell, name->string, v);
 
 	// We return an empty list for a nil value
 	if (!(v = ell_get (ell, name->string)))
@@ -1133,8 +1146,8 @@ ell_defn (ell_fn_cat) {
 		else
 			ell_buffer_append (&buf, args->string, args->len);
 	}
-	bool ok = !(ell->memory_failure |= buf.memory_failure)
-		&& ell_check (ell, (*result = ell_string (buf.s, buf.len)));
+	bool ok = !(ell->memory_failure |= buf.memory_failure) &&
+		ell_check (ell, (*result = ell_string (buf.s, buf.len)));
 	free (buf.s);
 	return ok;
 }
@@ -1172,8 +1185,8 @@ ell_defn (ell_fn_try) {
 		return true;
 
 	struct ell_v *msg;
-	if (ell->memory_failure
-	 || !ell_check (ell, (msg = ell_string (ell->error, strlen (ell->error)))))
+	if (ell->memory_failure ||
+		!ell_check (ell, (msg = ell_string (ell->error, strlen (ell->error)))))
 		return false;
 
 	free (ell->error); ell->error = NULL;

ell/stdlib.go

@@ -0,0 +1,513 @@
+//
+// Copyright (c) 2018, Přemysl Eric Janouch <p@janouch.name>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+//
+
+package ell
+
+import (
+	"bytes"
+	"fmt"
+	"os"
+	"os/exec"
+)
+
+// --- Standard library --------------------------------------------------------
+
+// EvalAny evaluates any value and appends to the result.
+func EvalAny(ell *Ell, body *V, arg *V) (result []V, ok bool) {
+	if body.Type == VTypeString {
+		return []V{*body}, true
+	}
+	var args []V
+	if arg != nil {
+		args = append(args, *arg.Clone())
+	}
+	if res, ok := ell.EvalBlock(body.List, args); ok {
+		return res, true
+	}
+	return nil, false
+}
+
+// NewNumber creates a new string value containing a number.
+func NewNumber(n float64) *V {
+	s := fmt.Sprintf("%f", n)
+	i := len(s)
+	for i > 0 && s[i-1] == '0' {
+		i--
+	}
+	if s[i-1] == '.' {
+		i--
+	}
+	return NewString(s[:i])
+}
+
+// Truthy decides whether any value is logically true.
+func Truthy(v *V) bool {
+	return v != nil && (len(v.List) > 0 || len(v.String) > 0)
+}
+
+// NewBoolean creates a new string value copying the boolean's truthiness.
+func NewBoolean(b bool) *V {
+	if b {
+		return NewString("1")
+	}
+	return NewString("")
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+func fnLocal(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) == 0 || args[0].Type != VTypeList {
+		return ell.Errorf("first argument must be a list")
+	}
+
+	// Duplicates or non-strings don't really matter to us, user's problem.
+	scope := ell.scopes[len(ell.scopes)-1]
+
+	values := args[1:]
+	for _, name := range args[0].List {
+		if len(values) > 0 {
+			scope[name.String] = *values[0].Clone()
+			values = values[1:]
+		}
+	}
+	return nil, true
+}
+
+func fnSet(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) == 0 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+
+	if len(args) > 1 {
+		result = []V{*args[1].Clone()}
+		ell.Set(args[0].String, &result[0])
+		return result, true
+	}
+
+	// We return an empty list for a nil value.
+	if v := ell.Get(args[0].String); v != nil {
+		result = []V{*v.Clone()}
+	} else {
+		result = []V{*NewList(nil)}
+	}
+	return result, true
+}
+
+func fnList(ell *Ell, args []V) (result []V, ok bool) {
+	return []V{*NewList(args)}, true
+}
+
+func fnValues(ell *Ell, args []V) (result []V, ok bool) {
+	return args, true
+}
+
+func fnIf(ell *Ell, args []V) (result []V, ok bool) {
+	var cond, body, keyword int
+	for cond = 0; ; cond = keyword + 1 {
+		if cond >= len(args) {
+			return ell.Errorf("missing condition")
+		}
+		if body = cond + 1; body >= len(args) {
+			return ell.Errorf("missing body")
+		}
+
+		var res []V
+		if res, ok = EvalAny(ell, &args[cond], nil); !ok {
+			return nil, false
+		}
+		if len(res) > 0 && Truthy(&res[0]) {
+			return EvalAny(ell, &args[body], nil)
+		}
+
+		if keyword = body + 1; keyword >= len(args) {
+			break
+		}
+		if args[keyword].Type != VTypeString {
+			return ell.Errorf("expected keyword, got list")
+		}
+
+		switch kw := args[keyword].String; kw {
+		case "else":
+			if body = keyword + 1; body >= len(args) {
+				return ell.Errorf("missing body")
+			}
+			return EvalAny(ell, &args[body], nil)
+		case "elif":
+		default:
+			return ell.Errorf("invalid keyword: %s", kw)
+		}
+	}
+	return nil, true
+}
+
+func fnMap(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 {
+		return ell.Errorf("first argument must be a function")
+	}
+	if len(args) < 2 || args[0].Type != VTypeList {
+		return ell.Errorf("second argument must be a list")
+	}
+
+	body, values := &args[0], &args[1]
+	for _, v := range values.List {
+		res, ok := EvalAny(ell, body, &v)
+		if !ok {
+			return nil, false
+		}
+		result = append(result, res...)
+	}
+	return []V{*NewList(result)}, true
+}
+
+func fnPrint(ell *Ell, args []V) (result []V, ok bool) {
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			PrintV(os.Stdout, &arg)
+		} else if _, err := os.Stdout.WriteString(arg.String); err != nil {
+			return ell.Errorf("write failed: %s", err)
+		}
+	}
+	return nil, true
+}
+
+func fnCat(ell *Ell, args []V) (result []V, ok bool) {
+	buf := bytes.NewBuffer(nil)
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			PrintV(buf, &arg)
+		} else {
+			buf.WriteString(arg.String)
+		}
+	}
+	return []V{*NewString(buf.String())}, true
+}
+
+func fnSystem(ell *Ell, args []V) (result []V, ok bool) {
+	var argv []string
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		argv = append(argv, arg.String)
+	}
+	if len(argv) == 0 {
+		return ell.Errorf("command name required")
+	}
+
+	cmd := exec.Command(argv[0], argv[1:]...)
+	cmd.Stdin = os.Stdin
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	// Approximation of system(3) return value to match C ell at least a bit.
+	if err := cmd.Run(); err == nil {
+		return []V{*NewNumber(0)}, true
+	} else if _, ok := err.(*exec.Error); ok {
+		return ell.Errorf("%s", err)
+	} else {
+		return []V{*NewNumber(1)}, true
+	}
+}
+
+func fnParse(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+
+	res, err := NewParser([]byte(args[0].String)).Run()
+	if err != nil {
+		return ell.Errorf("%s", err)
+	}
+	return []V{*NewList(res)}, true
+}
+
+func fnTry(ell *Ell, args []V) (result []V, ok bool) {
+	var body, handler *V
+	if len(args) < 1 {
+		return ell.Errorf("first argument must be a function")
+	}
+	if len(args) < 2 {
+		return ell.Errorf("second argument must be a function")
+	}
+	body, handler = &args[0], &args[1]
+	if result, ok = EvalAny(ell, body, nil); ok {
+		return
+	}
+
+	msg := NewString(ell.Error)
+	ell.Error = ""
+	return EvalAny(ell, handler, msg)
+}
+
+func fnThrow(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	return ell.Errorf("%s", args[0].String)
+}
+
+func fnPlus(ell *Ell, args []V) (result []V, ok bool) {
+	res := 0.
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		var value float64
+		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
+			return ell.Errorf("invalid number: %s", arg.String)
+		}
+		res += value
+	}
+	return []V{*NewNumber(res)}, true
+}
+
+func fnMinus(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+
+	var res float64
+	if n, _ := fmt.Sscan(args[0].String, &res); n < 1 {
+		return ell.Errorf("invalid number: %s", args[0].String)
+	}
+	if len(args) == 1 {
+		res = -res
+	}
+
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		var value float64
+		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
+			return ell.Errorf("invalid number: %s", arg.String)
+		}
+		res -= value
+	}
+	return []V{*NewNumber(res)}, true
+}
+
+func fnMultiply(ell *Ell, args []V) (result []V, ok bool) {
+	res := 1.
+	for _, arg := range args {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		var value float64
+		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
+			return ell.Errorf("invalid number: %s", arg.String)
+		}
+		res *= value
+	}
+	return []V{*NewNumber(res)}, true
+}
+
+func fnDivide(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+
+	var res float64
+	if n, _ := fmt.Sscan(args[0].String, &res); n < 1 {
+		return ell.Errorf("invalid number: %s", args[0].String)
+	}
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		var value float64
+		if n, _ := fmt.Sscan(arg.String, &value); n < 1 {
+			return ell.Errorf("invalid number: %s", arg.String)
+		}
+		res /= value
+	}
+	return []V{*NewNumber(res)}, true
+}
+
+func fnNot(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 {
+		return ell.Errorf("missing argument")
+	}
+	return []V{*NewBoolean(!Truthy(&args[0]))}, true
+}
+
+func fnAnd(ell *Ell, args []V) (result []V, ok bool) {
+	if args == nil {
+		return []V{*NewBoolean(true)}, true
+	}
+	for _, arg := range args {
+		result, ok = EvalAny(ell, &arg, nil)
+		if !ok {
+			return nil, false
+		}
+		if len(result) < 1 || !Truthy(&result[0]) {
+			return []V{*NewBoolean(false)}, true
+		}
+	}
+	return result, true
+}
+
+func fnOr(ell *Ell, args []V) (result []V, ok bool) {
+	for _, arg := range args {
+		result, ok = EvalAny(ell, &arg, nil)
+		if !ok {
+			return nil, false
+		}
+		if len(result) > 0 && Truthy(&result[0]) {
+			return result, true
+		}
+	}
+	return []V{*NewBoolean(false)}, true
+}
+
+func fnEq(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	etalon, res := args[0].String, true
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		if res = etalon == arg.String; !res {
+			break
+		}
+	}
+	return []V{*NewBoolean(res)}, true
+}
+
+func fnLt(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	etalon, res := args[0].String, true
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		if res = etalon < arg.String; !res {
+			break
+		}
+		etalon = arg.String
+	}
+	return []V{*NewBoolean(res)}, true
+}
+
+func fnEquals(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	var first, second float64
+	if n, _ := fmt.Sscan(args[0].String, &first); n < 1 {
+		return ell.Errorf("invalid number: %s", args[0].String)
+	}
+	res := true
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		if n, _ := fmt.Sscan(arg.String, &second); n < 1 {
+			return ell.Errorf("invalid number: %s", arg.String)
+		}
+		if res = first == second; !res {
+			break
+		}
+		first = second
+	}
+	return []V{*NewBoolean(res)}, true
+}
+
+func fnLess(ell *Ell, args []V) (result []V, ok bool) {
+	if len(args) < 1 || args[0].Type != VTypeString {
+		return ell.Errorf("first argument must be string")
+	}
+	var first, second float64
+	if n, _ := fmt.Sscan(args[0].String, &first); n < 1 {
+		return ell.Errorf("invalid number: %s", args[0].String)
+	}
+	res := true
+	for _, arg := range args[1:] {
+		if arg.Type != VTypeString {
+			return ell.Errorf("arguments must be strings")
+		}
+		if n, _ := fmt.Sscan(arg.String, &second); n < 1 {
+			return ell.Errorf("invalid number: %s", arg.String)
+		}
+		if res = first < second; !res {
+			break
+		}
+		first = second
+	}
+	return []V{*NewBoolean(res)}, true
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+var stdNative = map[string]Handler{
+	"local":  fnLocal,
+	"set":    fnSet,
+	"list":   fnList,
+	"values": fnValues,
+	"if":     fnIf,
+	"map":    fnMap,
+	"print":  fnPrint,
+	"..":     fnCat,
+	"system": fnSystem,
+	"parse":  fnParse,
+	"try":    fnTry,
+	"throw":  fnThrow,
+	"+":      fnPlus,
+	"-":      fnMinus,
+	"*":      fnMultiply,
+	"/":      fnDivide,
+	"not":    fnNot,
+	"and":    fnAnd,
+	"or":     fnOr,
+	"eq?":    fnEq,
+	"lt?":    fnLt,
+	"=":      fnEquals,
+	"<":      fnLess,
+}
+
+var stdComposed = `
+set unless { if (not (@1)) @2 }
+set filter { local [_body _list] @1 @2;
+ map { if (@_body @1) { @1 } } @_list }
+set for { local [_list _body] @1 @2;
+ try { map { @_body @1 } @_list } { if (ne? @1 _break) { throw @1 } } }
+
+set break { throw _break }
+
+# TODO: we should be able to apply them to all arguments
+set ne? { not (eq? @1 @2) }; set le? { ge? @2 @1 }
+set ge? { not (lt? @1 @2) }; set gt? { lt? @2 @1 }
+set <>  { not (= @1 @2)   }; set <=  { >= @2 @1  }
+set >=  { not (< @1 @2)   }; set >   { <  @2 @1  }`
+
+// StdInitialize initializes the ell standard library.
+func StdInitialize(ell *Ell) bool {
+	for name, handler := range stdNative {
+		ell.Native[name] = handler
+	}
+
+	p := NewParser([]byte(stdComposed))
+	program, err := p.Run()
+	if err != nil {
+		return false
+	}
+
+	_, ok := ell.EvalBlock(program, nil)
+	return ok
+}

go.mod

@@ -0,0 +1,7 @@
+module janouch.name/ell
+
+go 1.17
+
+require github.com/peterh/liner v1.1.0
+
+require github.com/mattn/go-runewidth v0.0.3 // indirect

go.sum

@@ -0,0 +1,4 @@
+github.com/mattn/go-runewidth v0.0.3 h1:a+kO+98RDGEfo6asOGMmpodZq4FNtnGP54yps8BzLR4=
+github.com/mattn/go-runewidth v0.0.3/go.mod h1:LwmH8dsx7+W8Uxz3IHJYH5QSwggIsqBzpuz5H//U1FU=
+github.com/peterh/liner v1.1.0 h1:f+aAedNJA6uk7+6rXsYBnhdo4Xux7ESLe+kcuVUF5os=
+github.com/peterh/liner v1.1.0/go.mod h1:CRroGNssyjTd/qIG2FyxByd2S8JEAZXBl4qUrZf8GS0=

interpreter.c

@@ -1,7 +1,7 @@
 /*
  * interpreter.c: test interpreter
  *
- * Copyright (c) 2017, Přemysl Janouch <p@janouch.name>
+ * Copyright (c) 2017, Přemysl Eric Janouch <p@janouch.name>
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted.
@@ -65,4 +65,3 @@ main (int argc, char *argv[]) {
 	ell_free (&ell);
 	return 0;
 }
-

repl.c

@@ -1,7 +1,7 @@
 /*
  * repl.c: test REPL
  *
- * Copyright (c) 2017, Přemysl Janouch <p@janouch.name>
+ * Copyright (c) 2017, Přemysl Eric Janouch <p@janouch.name>
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted.
@@ -17,8 +17,8 @@
  */
 
 #include "ell.c"
-#include <readline/readline.h>
 #include <readline/history.h>
+#include <readline/readline.h>
 
 static void
 run (struct ell *ell, struct ell_v *program) {